Simulating plasmaspheric field‐aligned density profiles measured with IMAGE/RPI: Effects of plasmasphere refilling and ion heating

Abstract

[1] The radio plasma imager (RPI) on board the IMAGE satellite measures electron density profiles along magnetic lines through radio sounding techniques. We simulate three density profiles measured by the RPI on 8 June 2001 using the field line interhemispheric plasma (FLIP) model and compare the modeled density profiles with observed profiles. While careful consideration of depletion of flux tubes followed by refilling over several days allows fair agreement between simulated and measured densities around the equator, the simulated densities in the off-equator regions remain significantly lower than those measured for all simulated flux tubes. It is shown that direct heating of ions in the plasmasphere during the plasmasphere refilling, in addition to heating through Coulomb collisions with hotter plasmaspheric electrons, can improve the agreement in the off-equator regions. The enhanced ion pressure in the high altitude part of magnetic field line due to the ion heating impedes the ionospheric inflow from both hemispheres toward the equator, giving rise to decreased transport of ionospheric ions into the equatorial region and thus increased density gradient along the magnetic field line.

Simulation of field-aligned H<sup>+</sup> and He<sup>+</sup> dynamics during late-stage plasmasphere refilling

“…This study differs from previous physics-based refilling simulations (Singh et al, 1986;Rasmussen and Schunk, 1988;Guiter and Gombosi, 1990;Tu et al, 2003;Singh and Horwitz, 1992, and references therein) in that both H + and He + are included, the source of plasmasphere ions is a comprehensive physics-based simulated ionosphere (see, e.g. Huba et al, 2000aHuba et al, ,b, 2005, refilling is initiated with the simulated loss of high-altitude plasma taking place over a period of hours (to simulate a storm), the complete ion dynamics along the direction of the field are computed for all ion species (i.e.…”

“…At the present time, both the data (Park, 1970;Sojka and Wrenn, 1985;Song et al, 1988;Singh and Horwitz, 1992;Lawrence et al, 1999;Su et al, 2001;Tu et al, 2003) and the models show that for a given flux tube, refilling begins with high-speed upflows from the two conjugate ionospheric sources, followed by a process in which the plasma is trapped or thermalized and, lastly, by a fluid-like evolution over a number of days. In general, early stage refilling (inflow and trapping; t<24 h) proceeds at a lower rate than late stage refilling (>24 h) (Lawrence et al, 1999).…”

“…Two past fluid-model refilling studies (Guiter and Gombosi, 1990;Tu et al, 2003), are similar to the present work in that realistic ionospheric sources are included. Guiter and Gombosi (1990) include the ion momentum terms for their two hydrodynamic ion species (H + and O + ) and include a realistic simulated ionosphere with several neutral and minor ion species.…”

“…While these were not elaborated upon, they do support the long refilling time scales determined by Rasmussen et al (1993) and bear some similarities to our present results. Tu et al (2003) describe refilling results from the field line interhemispheric plasma (FLIP) model (Richards and Wilkinson, 1998;St.-Maurice and Schunk, 1976). These simulations feature a tilted dipole geometry, a realistic ionosphere, and lengthy simulation times.…”

“…the inertial terms are included), and the field geometry uses a flexible dipole model of the earth's geomagnetic field that mimics the IGRF in the low-to mid-latitude ionosphere. While some of the past modeling work includes similar features, such as inertial ions (Guiter and Gombosi, 1990) or a realistic ionosphere (Guiter and Gombosi, 1990;Tu et al, 2003), none of them include all of these features.…”